Introduction

There is great interest in technologies to improve the accuracy and precision in placing implants for total hip arthroplasty (THA). Malik et al. (J Arthroplasty, 2010) showed that an imageless navigation system could be used to produce accurate measures of acetabular cup alignment compared to a CT-based alignment method using an imaging phantom. In this study we sought to compare the precision of an image-based navigation system with post-operative CT scans in a clinical patient cohort who received navigation-assisted THA.

Introduction: Navigation increases the precision and reproducibility of reconstruction in THR. It is important for the surgeon to be able to trust the reproducibility of the navigator and that navigated surgery should produce better results than those obtained by the surgeon by himself. The aim of this study is to determine the reproducibility and trustworthiness of a navigation system for acetabular reconstruction and to compare the precision of the navigator with that of the surgeon.

Materials and methods: A total of 101 THRs were carried out in 99 patients using image-free navigation. The precision and reproducibility of the navigator were measured with 30 postoperative CT scans. The blind estimates of the surgeons for inclination and anteversion were compared to the values of the navigator; the navigator was as accurate as the surgeon in 101 cases.

Results: The precision of the navigator for inclination was 4.4° with a reproducibility of 0.03 and for ante-version it was 4.1° with a reproducibility of 0.73. The precision of experienced surgeons for inclination was 11.5° and 12.3° for anteversion (less experienced surgeons had a precision for inclination of 13.1° and for anteversion of 13.9°).

Conclusions: Computer accuracy for the real value of a CT scan is always within 5°. The estimations of the surgeons with mechanical guides, experience and good judgment are about 12 degrees that of the navigation system. However the percentage of values 5° higher than the desired levels in experienced surgeons is seen in about 30% of cases (in less experienced surgeons, in about 50%). The computer can eliminate acetabular malposition to within about 5 degrees for desired values and in this way improve stability and wear.

Introduction: The long-term results of total hip replacement can be improved by accurate placement of the implants, leading to restoration of hip biomechanics and prevention impingement from of implant malposition. Pelvic obliquity from patient positioning during surgery prevents accurate intra-operative assessment of component placement. Computer navigation assisted total hip replacement can potentially eliminate these problems by providing feedback on prosthetic placement during surgery. The purpose of our study was to assess the accuracy of the component placement in computer navigation assisted THRs performed in our institution.

Methods: A total of 154 computer navigation assisted total hip arthroplasties performed between January 2004 and January 2005 were prospectively included in this study. Image free optical based navigation system (Navitrack™) was used. All procedures were performed by the senior author using MIS and open posterior approaches. Two independent observers performed analysis of the position of components and leg length discrepancy from standardized hip radiographs. Navigation values during surgery were compared with postoperative radiographic evaluation.

Results: The mean abduction and anteversion angles of acetabular component in postoperative radiographs were 41.4 ± 6.1 and 22.6 ± 3.8 degrees respectively, in comparison to the navigation values of 40.9 ± 4.0 and 22.9 ± 3.6 degrees respectively. The femoral neck offset and leg length discrepancy calculated from navigation were with in a mean of 1.5mm and 2.8mm, respectively. There was one complication consisting of a peri-prosthetic femoral fracture that was recognised during surgery and treated with revision of the femoral component to a long-stem prosthesis. There was no early post-operative dislocation or deep infection in this series.

Discussion: This study showed that computer navigation assisted THR provided predictable and reproducible results with accuracy in component placement and restorations of femoral neck offset and leg length.

Introduction: Technical and patient care improvements have occurred with the posterior mini-incision total hip replacement (THR). The hypothesis of this study was that these changes would provide better results for patients in the posterior mini incision surgery (MIS) THRs performed in our institution.

Methods: The clinical and radiographic results of 100 THRs performed with the posterior mini incision between January 2004 and October 2004 were compared with 100 mini incision THRs performed between December 2001 and September 2002. The second group was subjected to improved operative technique, the post-operative analgesia protocol, rehabilitation and patient advise. The acetabular cup abduction angle, anteversion angle, and stem varus/valgus alignment angle were measured in the post-operative radiographs in both groups. Pain score and Harris hip score were recorded at 6 weeks and 3 months. Statistical analysis was performed using Student 2-tailed t test, Chi-squared test and Wilcoxon-Mann-Whitney tests to compare the incision length, operative time, estimated blood loss, length of hospital stay, pain score and radiographic measurements between the two groups.

Results: The results showed that the component positions were not compromised in either group. There were statistical improvements in 2004 group with less estimated blood loss, decreased hospital stay, reduction of postoperative pain and opioid analgesic use and earlier muscle recovery. In 2004 group there were no complications of infection, dislocation, or sciatic palsy.

Discussion: The posterior mini-incision operation has shown improved results with experience and changes in technique and patient care treatment. We have continued our practice using this new technique.